Various entities define levels of autonomy that classify vehicles according to how autonomously the vehicles can operate. The National Highway Traffic Safety Administration (NHTSA) establishes five levels (0 to 4) and defines Level 2 as “automation of at least two primary control functions designed to work in unison to relieve the driver of control of those functions,” for example, “adaptive cruise control in combination with lane centering.” The Society of Automotive Engineers establishes six levels (0 to 5) and defines Level 2 autonomy as “the driving mode-specific execution by one or more driver assistance systems of both steering and acceleration/deceleration using information about the driving environment and with the expectation that the human driver perform all remaining aspects of the dynamic driving task.”
During Level 2 autonomous driving under either definition, a driver of a vehicle is expected to maintain attention on the task of driving the vehicle while the vehicle performs many of the actions of the driving task. This is a problem unique to semi-autonomous vehicles. If the vehicle has full autonomy, then the driver is not expected to maintain attention on the driving task. If the vehicle is nonautonomous, then the driver is constantly performing actions to control the vehicle, which thus maintains the attention of the driver.